The current wireless systems use either a Frequency Division Duplexing (FDD) or a Time Division Duplexing (FDD) approach. In an FDD approach, the uplink (mobile to base station link) and the downlink (base station to the mobile station link) use a different frequency. In general, the FDD systems make use of symmetric spectrum allocation (i.e. the bandwidth allocated to the downlink is the same as in the uplink). The examples of wireless systems using a FDD scheme are the 2G Global System for Mobile (GSM), 3G Universal Mobile Telecommunications System (UMTS) and 4G long term evolution (LTE) systems. Typically, the spectrum used for downlink transmissions are sufficiently separated in frequency from the spectrum used for uplink transmission to avoid interference between transmission and receiving operations at the same communication node.
In a TDD scheme, the uplink and the downlink share the same frequency band. However, the uplink and downlink transmissions happen at different times. In general, a frame of a given duration (T seconds) is divided into a downlink subframe (TDL) and an uplink subframe (TUL). Therefore, at a given time, the transmission happens either on the downlink or on the uplink. The Local Area Network (LAN) and Personal Area Network (PAN) standards, such as IEEE 802.11 and 802.15, as well as 3G/4G cellular systems, employ TDD.
In a full-duplex system, the uplink and the downlink share the same frequency band, and transmissions happen simultaneously in the same timeframe. A challenge of a full-duplex system is interference between the transmit and receive signals that are sent and received in the same timeframe.
Accordingly, there is a need for improved techniques in the full-duplex system.